Data center network research often demands a datacenter environment with a number of hosts, with virtualization support and switches to connect these hosts. A simple minimal fat tree topology, for instance, may well require 7 switches and at least 4 physical hosts.
Desirably, a simulation or emulation methodology should support at least the following basic requirements: support for end host virtualization and migration of virtual machines; full control over the network switches (software and layer-2, layer-3 configuration); and full control over the host software and hardware resources. Conventional simulation and emulation tools do not support all these requirements. In some cases, they may use network namespace and virtual ethernet pairs (veth) without supporting host virtualization and VM (virtual machine) migration. In other cases, host virtualization and VM migration are still not supported, and any developed code cannot realistically be deployed on a real switch. Limited control over host software and hardware resources also emerges as a problem.
If an attempt is made to construct a network of virtual machines with unsophisticated connections and interfaces, too much “weight” might emerge as a problem, and scalability might be limited to merely a handful of hosts and switches.